The role of body shape and mass in skimming on water

Over many years, there has been great practical interest in how solid bodies interact with and skim on liquid layers. In the present investigation, the focus is on the important role of body mass and shape in such skimming motions. Considering a thin two-dimensional solid body that impacts obliquely and then rebounds on a shallow inviscid water layer, we develop a mathematical model to predict quantitatively the duration and evolution of the body and fluid motions and indeed the success or failure of the whole skim. In the current setting, the shallow water layer thickness is small relative to the representative body length. The combined roles of increased mass and shape are found to be crucial, governed by a similarity solution. The relationship C ∼ M2/3 between scaled body curvature and mass is identified and highlighted. In particular, increased convex curvature of the underbody is found to alter the interactive pressure in such a way that it inhibits the occurrence of a super-elastic response in the exit vertical velocity and height of the body, and in effect enables a much heavier body to skim successfully provided the above relationship is maintained

A body in nonlinear near-wall shear flow:impacts, analysis and comparisons

Interaction between body motion and fluid motion is considered inside a nonlinear viscous wall layer, with this unsteady two-way coupling leading to impact of the body on the wall. The present paper involves a reduced system analysis which is shown to be consistent with computational solutions from direct numerical simulations for a basic flat-plate shape presented in an allied paper (Palmer & Smith, J. Fluid Mech., 2020). The occurrence of impact depends mainly on fluid parameters and initial conditions. The body considered is translating upstream or downstream relative to the wall. Subsequent analysis focusses on the unusual nature of the impact at the leading edge. The impacting flow structure is found to have two nonlinear viscous–inviscid regions lying on either side of a small viscous region. The flow properties in the regions dictate the lift and torque which drive the body towards the wall. Pronounced flow separations are common as the impact then cuts off the mass flux in the gap between the body and the wall; here, a nonlinear similarity solution sheds extra light on the separations. Comparisons are made between results from direct simulations and asymptotics at increased flow rate

Skimming impact of a thin heavy body on a shallow liquid layer

This study addresses the question of whether a thin, relatively heavy solid body with a smooth under-surface can skim on a shallow layer of liquid (for example water), i.e. impact on the layer and rebound from it. The body impacts obliquely onto the liquid layer with the trailing edge of the underbody making the initial contact. The wetted region then spreads along the underbody and eventually either retracts, generating a rebound, or continues to the leading edge of the body and possibly leads to the body sinking. The present inviscid study involves numerical investigations for increased mass ( M , in scaled terms) and moment of inertia ( I , proportional to the mass) together with an asymptotic analysis of the influential parameters and dynamics at different stages of the skimming motion. Comparisons between the asymptotic analysis and numerical results show close agreement as the body mass becomes large. A major finding is that, for a given impact angle of the underbody relative to the liquid surface, only a narrow band of initial conditions is found to allow the heavy-body skim to take place. This band includes reduced impact velocities of the body vertically and rotationally, both decreasing like M−2/3 , while the associated total time of the skim from entry to exit is found to increase like M1/3 typically. Increased mass thereby enhances the super-elastic behaviour of the skim

When a small thin two-dimensional body enters a viscous wall layer

If a body enters a viscous-inviscid fluid layer near a wall, then significant effects can be felt from the presence of incident vorticity, viscous forces and nonlinear forces. The focus here is on the response in the outer edge of such a wall layer. Nonlinear two-dimensional unsteady behaviour is examined through modelling, computation and analysis applied for a thin body travelling streamwise upstream or downstream or staying still relative to the wall. The wall layer with its balance between inviscid and viscous effects interacts freely with the body movement, causing relatively high magnitudes of pressure on top of the body and nonlinear responses in the gap between the body and the wall. The study finds explicit solutions for the motion of the body, separation of the flow arising near the wall and possible instabilities occurring over the length scale of any short body

Parameter inference in mechanistic models of cellular regulation and signalling pathways using gradient matching

A challenging problem in systems biology is parameter inference in mechanistic models of signalling pathways. In the present article, we investigate an approach based on gradient matching and nonparametric Bayesian modelling with Gaussian processes. We evaluate the method on two biological systems, related to the regulation of PIF4/5 in Arabidopsis thaliana, and the JAK/STAT signal transduction pathway

Stranded assets and the shipping industry

According to IMO forecasts, CO2 emissions from world shipping could double by the year 2050. Although shipping is in most cases the most efficient mode of transport per unit of transport supply, it is still heavily reliant on heavy fuel oil to power its propulsion. The IMO has introduced regulations to bring about reductions in the emissions of ships, including an Energy Efficiency Design Index which sets a mandatory CO2 intensity reduction target for new ships and imposing a sulphur regulation on ships operating in certain sea areas. At the same time, charterers are beginning to factor energy efficiency into their commercial decision-making through use of the EVDI (an approximation of EEDI). Exemplifying this trend, Cargill, Huntsman and UNIPEC UK publically announced in October 2012 that they would no longer charter the least efficient ships in the fleet. This regulatory environment, along with the uncertainty in energy prices and increased awareness of the industry’s carbon footprint, poses a threat to existing ships’ profitability and may result in certain ships becoming stranded assets. The objective of this paper is to identify the supply and demand-side risk factors contributing to existing ships becoming stranded assets, and to frame how an assessment could be carried out on the risk of stranded assets in the shipping industry

Ethics in fieldwork: Reflections on the unexpected

© 2014: Jane Palmer, Dena Fam, Tanzi Smith, Sarina Kilham, and Nova Southeastern University. Research involving fieldwork can present the researcher with ethical dilemmas not anticipated in institutional ethics approval processes, and which offer profound personal and methodological challenges. The authors' experiences of conducting qualitative fieldwork in four distinctly different contexts are used to illustrate some of these unexpected consequences and ethical dilemmas. Issues encountered included: compromised relationships with informants which develop in unforeseen ways; engagement with traumatized informants which lead to unexpected roles for the researcher such as confidante, dealing with new information that is critical to informants' futures but could undermine the research project, and the implications of ethical decisions for research design and analysis. In our shared reflection on the four case studies in this paper, we examine anticipatory rather than reactive ways of dealing with such ethical dilemmas. Preparation and critical reflection are found to be key tools in relating to field informants, dealing with the personal challenges of undertaking field work, and developing useful research outcomes after returning home. We conclude by suggesting some issues for field researchers to consider in addition to the concerns addressed in a standard university ethics approval process

Where’s the Data? Using Data Convincingly in Transdisciplinary Doctoral Research

Aim/Purpose The aim of this paper is to identify some of the issues in writing a transdisciplinary doctoral thesis and to develop strategies for addressing them, particularly focusing on the presentation of data and data analysis. The paper, based on the authors’ own experience, offers guidance to, and invites further comment from, transdisciplinary doctoral candidates, their supervisors and their examiners, as well as the broader field of interdisciplinary and multidisciplinary researchers. Background The paper uses the authors’ experience of writing four very different transdisciplinary doctoral theses to examine the diverse responses received from examiners and what this means for the thesis writing process. The theses and examiners’ reports span an array of disciplinary and transdisciplinary epistemologies, ontologies, and world views. Methodology A preliminary review of the examiners’ reports revealed a common concern with the definition of ‘data’ and with ‘data analysis’. The examiners’ reports were then more formally coded and thematized. These themes were then used to reflect critically on the four theses, within a broad interpretive framework based on the idea of writing ‘convincingly’, and in light of current literature on the meaning of ‘data’ and the idea and aims of transdisciplinarity. Contribution The paper offers specific strategies for doctoral candidates, their supervisors, and examiners in working with the burgeoning number of doctoral research projects that are now taking place in the transdisciplinary space. Findings Doctoral candidates engaged in transdisciplinary research need to define what they mean by data and make data visible in their research, be creative in their conceptions of data and in how they communicate this to examiners, specify the quality criteria against which they wish their work to be assessed and hold discussions with their supervisors about examiner appointments and briefing, and communicate to examiners the special value of transdisciplinary research and the journey on which it takes the researcher. Our conclusion connects these findings to the development of an emerging concept of transdisciplinary research writing. Recommendations for See below under ‘Recommendations for Researchers’ (For the purpose of Practitioners this paper, practitioners are the researchers). Recommendations The paper makes the following recommendations for transdisciplinary for Researchers doctoral researchers: • Make the data visible and argue for the unique or special way in which the data will be used • Make clear the quality criteria against which you expect the work to be judged • Be creative and explore the possibilities enabled by a broad interpretation of ‘data’ • Transdisciplinary research is transformative. Communicate this to your examiner. Impact on Society As more complex and ‘wicked’ problems in the world are increasingly addressed through transdisciplinary research, it is important that doctoral research in this area be encouraged, which continues to develop transdisciplinary theoretical frameworks, methodologies and applications. The strategies proposed in this paper will help to ensure the development of high quality transdisciplinary researchers and a greater understanding of the value of transdisciplinary research in the wider research community. It also draws attention to the potential benefits of similar strategies in multidisciplinary and interdisciplinary research. Future Research Further exploration is needed of how researchers across disciplines can ‘talk’ to one another to resolve complex problems, and how the solitary transdisciplinary scholar, such as the doctoral student, can effectively communicate their research contribution to others. These issues could also be explored for multidisciplinary and interdisciplinary research teams

Hormone-Type Herbicides--Safe Use and Precautions.

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